Fainting, also known as syncope, is the sudden loss of consciousness. In most cases, fainting is not dangerous – unless it is complicated by a fall or other injury – and the person recovers quickly.
In some cases, however, fainting can be an indicator that something is wrong with the heart and that blood is not being pumped properly.
During pregnancy in particular, a woman’s body undergoes a lot of changes. These include hormonal changes, an increase in the amount of blood in the body, changes to the structure of the heart and in heart rate. These can make pregnant women more likely to experience dizziness and fainting.
However, most of the information about fainting during pregnancy is anecdotal; we don’t really know how often it occurs and whether it has any consequences for the health of the child or the mother.
My colleagues and I therefore decided to answer these questions using a large cohort of almost 500 000 women who gave birth over a 10-year period between 2005 and 2014.
Risk of early delivery and medical problems
We found that fainting during pregnancy is a relatively rare event and occurs in about 1% of pregnancies, but its occurrence is slowly increasing over time.
Our study included 4 667 pregnancies with a fainting episode. Women who fainted were slightly younger, single, pregnant with their first child and had a history of fainting prior to pregnancy compared with women who did not faint during pregnancy.
In a third of these pregnancies the fainting episode occurred in the first trimester. Only 8% of these pregnancies had more than one episode of fainting.
Women who fainted during the first trimester had a slightly higher risk of delivering the baby early – before the normal 37 weeks of gestation – than women who did not faint or those who fainted during the second or third trimester.
Children born to mothers with multiple fainting episodes during pregnancy had more medical problems at birth (4.9%) compared to children born in women who did not faint during pregnancy (2.9%).
Associated with heart conditions in mother
When we looked at the year following delivery, we found that women who fainted during pregnancy were more likely to seek medical care for heart conditions such as an irregular heart beat (cardiac arrhythmias).
We suggest that women who faint during pregnancy should contact their health-care providers right away, which is probably what most pregnant women are inclined to do.
Pregnancy is increasingly being likened to a natural stress test that a woman undergoes. Studies have shown that other complications that occur in pregnancy – such as pre-eclampsia and gestational diabetes mellitus – identify women who may be at a higher risk of future heart problems.
Our study suggests that the heart health of women who faint should also be monitored closely, both during pregnancy and in the post-partum period.
This research is the first to systematically study the occurrence and outcomes associated with fainting during pregnancy.
Although large, its findings are based on just one group of women in a single province in Canada. More studies in other pregnant populations are needed to see whether they find similar results to ours.